I wouldn’t accept that as normal. In well-run organizations, when there is a regular, ongoing need for evening or overnight coverage, it’s provided by people scheduled to work during those hours, who are selected and trained to be able to handle most situations on their own.

After-hours calls should come infrequently, or in situations where someone’s personal involvement (for example, as the engineer with primary responsibility for a particular component or its maintenance) is indispensable.

In my experience, things that need a lot of unplanned attention are more likely to fail, if they haven’t already, in ways that have other unacceptable consequences. Fixing them should be a priority for this reason, too.

You haven’t mentioned why you keep getting paged. Is it the same problem repeatedly, or lots of different problems? Is there any hope of addressing the underlying causes?